Optical recording medium and method for producing such an optical recording medium

ABSTRACT

The present invention relates to a method for producing an optical recording medium. In the method, on the surface of a recording layer formed by spin-coating a first coating solution containing a photo-isomerizable component, a second coating solution that contains a photo-isomerizable component that can be isomerized by radiation having the same wavelength as radiation used for isomerizing the photo-isomerizable component contained in the recording layer and incapable of dissolving the recording layer is spin-coated to form an intermediate layer. Since the intermediate layer thus formed cannot be dissolved by the first coating solution, a recording layer is further laminated on this layer. Thus, it becomes possible to make the recording layer thicker and also to provide a high-density recording characteristic.

BACKGROUND OF THE INVENTION CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese patentApplication No. 2003-081289, the disclosure of which is incorporated byreference herein.

1. Field of the Invention

The present invention relates to an optical recording medium and amethod for producing the optical recording medium. More particularly,the invention relates to an optical recording medium provided with aplurality of recording layers on which information can be recordedholographically are laminated, and a method for producing the opticalrecording medium by spin-coating.

2. Description of the Related Art

Conventionally, rewritable optical disk recording media, such as 12cm-diameter DVD-RAM capable of high-density, double-sided recording of5.2 GByte (Gigabyte) with a phase change system, have already beenwidely used. However, in these optical disk recording media, since dataare recorded in a plane, high-density recording is restricted bydiffraction limit of radiation and has come close to a physicallimitation. In order to achieve a higher recording capacity, athree-dimensional (volume) recording system including a depth directionis required. With respect to the above-mentioned volume-type recordingmedium, a volume holography memory capable of volume-recording hologramlattices has been regarded as a prospective medium.

Here, in order to achieve a large capacity in the volume holographymemory, “a thicker recording layer” is the most important factor. Ingeneral, the thicker the hologram, the narrower the incident angleconditions for allowing diffraction, and only a slight offset from Braggconditions causes diffraction radiation to disappear. The multiple anglemethod in the volume holography memory utilizes this angle selectivity.In other words, a plurality of holograms are formed in the same volume,and by controlling the incident angle of reading radiation, it becomespossible to read a desired hologram without crosstalk. In this manner,by increasing the film thickness of the recording layer so as to improvethe angle selectivity, the multiplicity can be increased so that therecording capacity is increased.

In DVDs and the like, in general, the spin-coating has been used forforming a recording layer. In the spin-coating, a coating solution isdropped onto portions near center on a rotating disk, the coatingsolution, driven by centrifugal force, flows and reaches the peripheryof the disk to form a film, excessive coating solution flies out fromthe periphery of the disk, then the solvent is removed from the film.For example, recording layers and non-recording layers are laminatedalternately by using the spin-coating to form a multi-layer holographicmemory (see Japanese Patent Application Laid-Open (JP-A) No. 11-250496).In this example, a solution A prepared by dissolving polymer containinga photo-reactive component in pyridine is spin-coated to form arecording layer having a thickness of 1 μm, and on this recording layer,a solution B prepared by dissolving polyvinyl alcohol in water isspin-coated to form a non-recording layer having a thickness of 8 μm.

However, it is very difficult to form a recording layer having athickness of several tens μm or more to be used for the volumeholography through single spin-coating process. Since the holographymemory disclosed in JP-A No. 11-250496 is not used for multiplexrecording, the thickness of the recording layer formed in the methoddisclosed in JP-A No. 11-250496 is as thin as approximately 1 μm.Further, since holograms recorded in the laminated recording medium areformed in the respective recording layers for avoiding crosstalks, thismethod is not suitable for the volume holography.

SUMMARY OF THE INVENTION

Considering the conventional problems, an object of the presentinvention is to provide a method for producing an optical recordingmedium, which can produce an optical recording medium provided with athick recording layer by employing a spin-coating process. Anotherobject of the invention is to provide an optical recording mediumcapable of forming volume holograms over the entire laminated thick filmand a method for producing an optical recording medium which can producesuch an optical medium.

A method for producing an optical recording medium of the invention forachieving the objects can be employed for producing an optical recordingmedium in which a plurality of recording layers on which information canbe recorded holographically are laminated on a disc-shaped substratewith intermediate layers between the recording layers. The method ischaracterized by the steps of: applying a first coating solutioncontaining a photo-isomerizable component onto a surface of thehorizontally-held substrate or intermediate layer; the coating solutionis driven toward and flied out from the periphery of the substrate by acentrifugal force generated by rotating the substrate while the film isdried, to form the recording layer; applying to the surface of therecording layer a second coating solution incapable of dissolving therecording layer and containing a photo-isomerizable component that canbe isomerized by radiation having the same wavelength as radiation usedfor isomerizing a photo-isomerizable component contained in therecording layer; and the second coating solution is driven toward andflied out from the periphery of the substrate by a centrifugal forcegenerated by rotating the substrate while the film is dried, so that anintermediate layer that cannot be dissolved by the first coatingsolution is formed.

In the method for producing the optical recording medium of theinvention, on the surface of the recording layer formed by spin-coatingthe first coating solution containing a photo-isomerizable component, asecond coating solution that does not dissolve the recording layer isspin-coated to form an intermediate layer. Since the intermediate layerthus formed is not dissolved by the first coating solution, a recordinglayer is further laminated on this layer. Thus, it is possible to makethe recording layer thicker by using the intermediate layer.

Moreover, the intermediate layer contains a photo-isomerizable componentthat can be isomerized by radiation having the same wavelength as thatused for isomerizing a photo-isomerizable component contained in therecording layer so that holograms can be recorded in both of therecording layers and the intermediate layers sandwiched between therecording layers. The photo-isomerizable component contained in theintermediate layer may be the same as or different from thephoto-isomerizable component contained in the recording layer. Theintermediate layer containing the photo-isomerizable component enablesinformation to be recorded also in the intermediate layer to increasethe recording capacity.

In the method for producing an optical recording medium, a plurality ofrecording layers and intermediate layers preferably containphoto-isomerizable components that can be photo-isomerized by radiationhaving the same wavelength. With such a constitution, recording andreproducing processes for information recorded on the respectiverecording layers and intermediate layers can be carried out by using asingle radiation source, thereby making it possible to simplify thestructure of the recording and reproducing systems at low costs.Consequently, it becomes possible to provide a wider window for opticalprecision.

Moreover, the thickness of the intermediate layer is preferably madethinner than that of the recording layer, and set to ¼ or less of theincident wavelength λ. By making the thickness of the intermediate layerthinner than the thickness of the recording layer, the recording layeris further made thicker. Moreover, with the intermediate layer having athickness of ¼ or less of the incident wavelength λ, the incidentradiation can pass through without reflection on the interface. Hence,recording and reproducing processes are not influenced by thereflection.

Furthermore, the viscosity of the first coating solution is preferablymade higher than that of the second coating solution. By making theviscosity of the first coating solution higher, the recording layer canbe further made thicker. The thickness of the film in which therecording layers and the intermediate layers are laminated is preferably10 μm or more.

Here, the photo-isomerizable component may be a polymer componentcontaining a photo-isomerizable organic atomic group or a polymercomponent in which photo-isomerizable organic molecules are dispersed.With respect to the photo-isomerizable organic atomic group or thephoto-isomerizable organic molecules, azobenzene is particularlypreferable.

Moreover, the optical recording medium of the invention for achievingthe objects is an optical recording medium in which a plurality ofrecording layers on which information can be recorded holographicallyare laminated on a disc-shaped substrate. The optical recording mediumis characterized in that the optical recording medium comprisesalternate lamination of recording layers each containing aphoto-isomerizable component that records holograms byphoto-isomerization; and intermediate layers each of which contains aphoto-isomerizable component that can be isomerized by radiation havingthe same wavelength as radiation used for isomerizing thephoto-isomerizable component contained in the recording layer and iscomposed of a material that can be dissolved or dispersed in a solventthat does not dissolve the recording layer.

In the optical recording medium of the invention, the intermediate layercontains a photo-isomerizable component that can be isomerized byradiation having the same wavelength as radiation used for thephoto-isomerizable component contained in the recording layer;therefore, holograms can be recorded in both of the recording layers andthe intermediate layer sandwiched between the recording layers. In otherwords, the intermediate layer functions virtually as a recording layer.For example, the recording layers and the intermediate layers can belaminated alternately by forming the recording layer out of awater-insoluble material and forming the intermediate layer out of amaterial that can be dissolved or dispersed in water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view that shows the external appearance of anoptical recording medium according to the present invention.

FIG. 2 is a cross-sectional view that shows one example of a layerstructure of an optical recording medium according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description will discuss embodiments of a method forproducing an optical recording medium of the present invention.

An embodiment of the invention is a method (U) for producing an opticalrecording medium comprising a plurality of recording layers on adisc-shaped substrate on which information can be recordedholographically, and intermediate layers provided between the recordinglayers, the method comprising:

applying a first coating solution containing a photo-isomerizablecomponent, which records information holographically byphoto-isomerization onto a surface of one of the substrate or theintermediate layer, which is being held horizontally;

allowing the coating solution to flow toward a periphery of thesubstrate by a centrifugal force generated by rotating the substratewhile a film is dried, to provide the recording layer;

applying a second coating solution containing a photo-isomerizablecomponent that can be isomerized by radiation having the same wavelengthas radiation used for isomerizing a photo-isomerizable componentcontained in the recording layer and incapable of dissolving therecording layer, to a surface of the recording layer; and

allowing the second coating solution to flow toward the periphery of thesubstrate by a centrifugal force generated by rotating the substratewhile a film is dried, to provide an intermediate layer that cannot bedissolved by the first coating solution.

Another embodiment of the invention is the method (U) for producing anoptical recording medium, wherein each of the recording layers containphoto-isomerizable components that can be isomerized by radiation havinga same wavelength.

Another embodiment of the invention is the method (U) for producing anoptical recording medium, wherein a thickness of the intermediate layeris thinner than a thickness of the recording layer.

Another embodiment of the invention is the method (U) for producing anoptical recording medium, wherein a thickness of the intermediate layeris no more than ¼ of an incident wavelength λ.

Another embodiment of the invention is the method (U) for producing anoptical recording medium, wherein a viscosity of the first coatingsolution is higher than a viscosity of the second coating solution.

Another embodiment of the invention is the method (U) for producing anoptical recording medium, wherein the photo-isomerizable component is apolymer component containing a photo-isomerizable organic atomic groupor a polymer component in which photo-isomerizable organic molecules aredispersed.

Another embodiment of the invention is the method (U) for producing anoptical recording medium, wherein the photo-isomerizable component is apolymer component containing a photo-isomerizable organic atomic groupor a polymer component in which photo-isomerizable organic molecules aredispersed, and the photo-isomerizable organic atomic group or thephoto-isomerizable organic molecules are azobenzene.

Another embodiment of the invention is the method (U) for producing anoptical recording medium, wherein a laminated film constituted by therecording layers and the intermediate layers has a thickness of at least10 μm.

Another embodiment of the invention is an optical recording medium (V)comprising a plurality of recording layers on which information can berecorded holographically on a disc-shaped substrate, wherein

the recording layers each contain photo-isomerizable components thatrecord holograms through photo-isomerization, and

intermediate layers, each of which contains photo-isomerizablecomponents that can be isomerized by radiation having a same wavelengthas radiation used for isomerizing the photo-isomerizable componentcontained in the recording layer and is composed of a material that canbe one of dissolved or dispersed in a solvent that does not dissolve therecording layer,

are laminated alternately in the optical recording medium.

Another embodiment of the invention is the optical recording medium (V),wherein the recording layer is composed of a water-insoluble materialand the intermediate layer is composed of a material that cannot bedissolved in water.

Another embodiment of the invention is the optical recording medium (V),wherein the recording layers contain photo-isomerizable components thatcan be isomerized by radiation having the same wavelength.

Another embodiment of the invention is the optical recording medium (V),wherein a thickness of the intermediate layer is thinner than thethickness of the recording layer.

Another embodiment of the invention is the optical recording medium (V),wherein a thickness of the intermediate layer is no more than ¼ of anincident wavelength λ.

Another embodiment of the invention is the optical recording medium (V),wherein the photo-isomerizable component is a polymer componentcontaining a photo-isomerizable organic atomic group or a polymercomponent in which photo-isomerizable organic molecules are dispersed.

Another embodiment of the invention is the optical recording medium (V),wherein the photo-isomerizable component is a polymer componentcontaining a photo-isomerizable organic atomic group or a polymercomponent in which photo-isomerizable organic molecules are dispersed,and the photo-isomerizable organic atomic group or thephoto-isomerizable organic molecules are azobenzene.

Still another embodiment of the invention is the optical recordingmedium (V), wherein a laminated film constituted by the recording layersand the intermediate layers has a thickness of at least 10 μm.

[Optical Recording Medium]

First, the structure of an optical recording medium obtained by theproduction method of the invention is explained.

As shown in FIG. 1, an optical recording medium 35 is a disc-shapedrecording medium having a center hole 10 formed in the center. As shownin FIG. 2, the optical recording medium 35 is constituted by a pluralityof recording layers 14 and a plurality of intermediate layers 16 thatare laminated alternately on a disc-shaped transparent substrate 12.FIG. 2 shows an example in which five recording layers 14 and fourintermediate layers 16 are provided, however, the number of thelaminated layers is not limited to this example.

With respect to the transparent substrate 12, a substrate, such as aquartz substrate, a glass substrate and a plastic substrate, can beused. Here, “transparent” refers to the fact that the substrate istransparent with respect to recording radiation and reproducingradiation. With respect to the material for the plastic substrate,examples thereof include polycarbonate; acrylic resins such aspolymethyl methacrylate; vinylchloride-based resins such aspolyvinylchloride and a vinylchloride copolymer; epoxy resins; amorphouspolyolefin and polyester; all of which are made to have a low index ofdouble refraction. From the viewpoint of moisture resistance,dimensional stability and price, polycarbonate is particularlypreferable. The thickness of the transparent substrate 12 is preferablyfrom 0.01 to 5 mm. Here, the transparent substrate 12 may be providedwith a concave and convex pattern (pregrooves) that represents guidegrooves for use in tracking or information such as address signals.

Holograms can be recorded in the recording layers 14 and theintermediate layers 16 by changing the refractive indexes or absorptioncoefficients of the recording layers 14 and the intermediate layers 16through photo-isomerization. The recording layers 14 or the intermediatelayers 16 may be composed of any material as long as it maintains thechanged refractive indexes or absorption coefficients at normaltemperature. Examples of the preferable material includephoto-responsive materials that exhibit photo-induced double refraction.Those materials that exhibit photo-induced double refraction respond toa polarizing state of incident radiation, and can record the polarizingdirection of the incident radiation. Here, the optical recording mediumin which photo-induced double refraction holograms corresponding to thepolarization distribution can be recorded is referred to as an opticalrecording medium sensitive to polarization.

As material that exhibits photo-induced double refraction, a polymer ora polymer crystal having a photo-isomerizable group on its side chain,or a polymer in which photo-isomerizable molecules are dispersed, ispreferably used. With respect to the photo-isomerizable group ormolecules, for example, those materials having an azobenzene skeletonare preferably used.

The following description will discuss the principle of photo-induceddouble refraction, using azobenzene as an example. As shown in thefollowing chemical formulae, azobenzene is allowed to exhibit atrans-cis photo-isomerizing property when irradiated with radiation.Prior to the irradiation of a photorecording layer with radiation, manytrans-state azobenzene molecules exist in the photorecording layer.These molecules are randomly oriented, and are isotropic from amacroscopic viewpoint. When linearly polarizing radiation is irradiatedto the photorecording layer in a predetermined direction indicated by anarrow, a trans1-state molecule having an absorption axis in the sameorientation as the polarizing orientation is selectivelyphoto-isomerized into a cis-state. Molecules which have been relaxed totake a trans2-state having an absorption axis orthogonal to thepolarizing orientation, no longer absorb radiation, and are fixed in thestate. Consequently, from a macroscopic viewpoint, the anisotropy of theabsorption coefficient and refractive index, that is, dichroism anddouble refraction, are induced. In general, these characteristics arereferred to as photo-induced double refraction, photo-induced dichroismor photo-induced anisotropy. By applying circular-polarizing ornon-polarizing radiation, the excited anisotropy can be erased.

The orientation of such a polymer having a photo-isomerizable group isalso changed by the photo-isomerization to induce greater doublerefraction. The double refraction thus induced is stable at atemperature lower than the glass transition temperature of the polymer,and preferably used for hologram recording.

Preferable examples of the materials constituting the recording layer 14include polyester (hereinafter, referred to as “azopolymer”) havingazobenzene in its side chain, which is represented by the followingformula (1). Azobenzene on the side chain of this polyester isphoto-isomerized to give photo-induced anisotropy. The intensity andpolarizing direction of signal radiation can be recorded as holograms byusing the polyester due to the photo-induced anisotropy. Amongpolyesters of this kind, in particular, polyesters having cyanobenzeneon their side chain are preferably used. (“Holographic recording andretrieval of polarized radiation by use of polyester containingcyanoazobenzene units in the side chain”, K. Kawano. T. Ishii, J.Minabe, Ti. Niitsu, Y. Nishikata and K. Baba, Opt. Lett. Vol. 24 (1999)pp. 1269–1271).

In the general formula (1), X represents a cyano group, a methyl group,a methoxy group or a nitro group, and Y represents a divalent connectinggroup that forms an ether bond, a ketone bond or a sulfone bond. Each of1 and m is an integer of 2 to 18, more preferably, 4 to 10, and n is aninteger of 5 to 500, more preferably, 10 to 100.

The film thickness of each recording layer 14 is preferably in a rangeof 1 to 100 μm, more preferably, 5 to 30 μm. Moreover, the total of thefilm thicknesses of the recording layers 14 in the entire medium ispreferably in the range of 10 to 1000 μm, more preferably, 100 to 500μm. The method for providing the above-mentioned recording layer 14 willbe described later.

In order to increase the total of the film thicknesses of the recordinglayers in the entire medium and impart a function of recording volumeholograms to the recording medium by laminating recording layers 14,intermediate layers 16 are inserted between the recording layers 14.With respect to the material to be used for forming the intermediatelayer 16, examples thereof include water-soluble materials such aspolyvinyl alcohol (PVA), polyethylene glycol, cationized cellulose,sodium carboxymethylcellulose, water-soluble chitosan, gelatin, amyloseand pectinic acid. Moreover, as described above, a hologram recordingmaterial is added to the intermediate layers 16 as well as recordinglayers 14. Since the hologram recording material is contained in theintermediate layer 16, the medium as a whole is utilized as a recordinglayer.

The thickness of the intermediate layer 16 is preferably made thinnerthan that of the recording layer 14. More specifically, the thickness ofthe intermediate layer 16 is preferably from 0.05 to 0.2 μm, morepreferably, from ¼ or less of the incident wavelength λ. By making theintermediate layer 16 thinner, the recording layer 14 is virtually madethicker. By making the intermediate layer 16 thinner to ¼ or less of theincident wavelength λ, the reflection on the interface is prevented. Themethod for providing the above-mentioned intermediate layer 16 will bedescribed layer.

[Method for Producing an Optical Recording Medium]

The following description will discuss the method for producing anoptical recording medium by which the above-mentioned optical recordingmedium is produced. In the production method of the invention, thefollowing “forming process of a recording layer” and “forming process ofan intermediate layer” are repeated alternately to produce an opticalrecording medium in which recording layers and intermediate layers arealternately laminated.

(Forming Process of Recording Layers)

The recording layer 14 is provided by spin-coating a coating solutionfor the recording layer on the surface of a transparent substrate 12 oran intermediate layer 16. The spin-coating process is carried out bydropping the coating solution on a portion near center on a rotatingdisc-shaped transparent substrate 1; the coating solution is driventoward the periphery of the transparent substrate 12 by centrifugalforce to form a film; an excessive coating solution is flied out fromthe periphery of the transparent substrate 12; and the solvent isremoved from the film.

The coating solution for the recording layer is prepared by dissolvingthe above-mentioned hologram recording material in an appropriatesolvent. With respect to the solvent used for preparing the coatingsolution, examples thereof include: tetrahydrofran (THF), chloroform,methylene chloride and the like. These may be used alone, or two of moreof these may be used in combination. The solvent is appropriatelyselected by considering the solubility of the material used in therecording layers 14 and the solubility of the material constituting theintermediate layers 16, in order to completely dissolve the material tobe used in the recording layer 14 and also to prevent the intermediatelayer 16 from being dissolved during coating.

The concentration of the coating solution for the recording layer ispreferably from 0.01 to 50% by mass, more preferably, from 0.5 to 10% bymass, in order to form a uniform and thick film. The hologram recordingmaterial and the like are evenly dissolved in the solvent by using amethod such as an ultrasonic treatment, a homogenizer treatment, and aheating treatment. Here, various additives, such as an antioxidant, a UVabsorbing agent, a plasticizer and a lubricant may be further added tothe coating solution, depending on its objects.

The amount of the coating solution to be coated is preferably from 100to 5000 ml/m², more preferably, from 200 to 1000 ml/m². The revolutionsrate of the substrate in a period from the addition of the coatingsolution to the completion of the drying process is preferably from 10to 50000 rpm, more preferably, from 100 to 10000 rpm. The coatingtemperature is preferably from room temperature to 130° C., morepreferably, from 20 to 100° C. Moreover, the relative humidity at thetime of coating is preferably from 5 to 80% RH, more preferably, from 5to 70% RH. Moreover, a drying process may be further added thereto.

(Forming Process of Intermediate Layers)

The intermediate layer 16 is provided by spin-coating a coating solutionfor the intermediate layer on the surface of the recording layer 14. Thecoating solution for the intermediate layer is prepared by dissolvingthe above-mentioned materials that will constitute the intermediatelayer in an appropriate solvent. With respect to the solvent used forpreparing the coating solution, a solvent that does not dissolve thematerials constituting the recording layer 14 is required. An example ofsuch a solvent is water.

The concentration of the coating solution for the intermediate layer ispreferably from 0.01 to 50% by mass, more preferably, from 0.1 to 10% bymass.

The amount of the coating solution to be coated is preferably from 100to 5000 ml/m², more preferably, from 200 to 1000 ml/m². The revolutionrate of the substrate in a period from the addition of the coatingsolution to the completion of the drying process is preferably from 10to 50000 rpm, more preferably, from 100 to 10000 rpm. The coatingtemperature is preferably from room temperature to 130° C., morepreferably, from 20 to 100° C. Moreover, the relative humidity at thetime of coating is preferably from 5 to 80% RH, more preferably, from 5to 70% RH. Moreover, a drying process may be further added thereto.

As described above, the coating solution that does not dissolve therecording layer is spin-coated on a surface of the recording layerformed by the spin-coating, to form an intermediate layer. And arecording layer can be further laminated on the surface of theintermediate layer thus formed; therefore, it becomes possible to makethe laminated film thicker by using the intermediate layers.

In the resulting optical recording medium, the intermediate layer alsocontains a hologram recording material that can be isomerized to recordholograms upon application of radiation having the same wavelength asradiation used for isomerizing the hologram recording material containedin the recording layer; thus, the holograms are recorded in therecording layers and the intermediate layer sandwiched between therecording layers. Here, in order to record volume-type holograms, atotal thickness of the film constituted by the recording layers and theintermediate layers is preferably at least 10 μm.

According to the method for producing the optical recording medium ofthe invention, the coating solution that does not dissolve the recordinglayer is spin-coated on the surface of the recording layer, to form theintermediate layer. And a recording layer can be further laminated onthe surface of the intermediate layer thus formed; therefore, theresulting effect is that the recording layer is made thicker by usingthe intermediate layers.

Moreover, according to the optical recording medium of the invention andthe producing method thereof, the intermediate layer contains aphoto-isomerizable component that can be isomerized upon application ofradiation having the same wavelength as radiation used for isomerizingthe photo-isomerizable component contained in the recording layer.Therefore, it is possible to form volume-type holograms over the entirethick film in which the layers are laminated.

1. An optical recording medium comprising a plurality of recordinglayers on which information is recorded holographically on a disc-shapedsubstrate, wherein the recording layers each contain photo-isomerizablecomponents that record holograms through photo-isomerization, andintermediate layers, each of which contains photo-isomerizablecomponents that are isomerized by radiation having a same wavelength asradiation used for isomerizing the photo-isomerizable componentcontained in the recording layer and is composed of a material that isone of dissolved or dispersed in a solvent that does not dissolve therecording layer, are laminated alternately in the optical recordingmedium.
 2. An optical recording medium according to claim 1, wherein therecording layer is composed of a water-insoluble material and theintermediate layer is composed of a material that cannot be dissolved inwater.
 3. An optical recording medium according to claim 1, wherein therecording layers contain photo-isomerizable components that can beisomerized by radiation having the same wavelength.
 4. An opticalrecording medium according to claim 1, wherein a thickness of theintermediate layer is thinner than the thickness of the recording layer.5. An optical recording medium according to claim 1, wherein a thicknessof the intermediate layer is no more than ¼ of an incident wavelength λ.6. An optical recording medium according to claim 1, wherein thephoto-isomerizable component is a polymer component containing aphoto-isomerizable organic atomic group or a polymer component in whichphoto-isomerizable organic molecules are dispersed.
 7. An opticalrecording medium according to claim 6, wherein the photo-isomerizableorganic atomic group or the photo-isomerizable organic molecules areazobenzene.
 8. An optical recording medium according to claim 1, whereina laminated film constituted by the recording layers and theintermediate layers has a thickness of at least 10 μm.